This invention relates to a method for sending a notice of failure detection. More particularly, this invention relates to a method for sending a notice of failure detection in a system wherein apparatuses A and B are connected by a pair of two independent transfer paths, that is, a transfer path for transmitting data from the apparatus A to the apparatus B and a transfer path for transmitting the data from the apparatus B to the apparatus A, and the data are communicated mutually between these two apparatuses.
In apparatuses for executing data communication by using twist-pair cables or optical fiber cables in accordance with the system stipulated by IEEE802.3 (IEEE: The Institute of Electrical and Electronics Engineers), two apparatuses are point-to-point connected by one cable. The term “apparatus” used hereby means an inter-network apparatus such as a computer, a hub accommodating therein a computer, a rooter, a LAN switch, and so forth. Let's consider, for example, a case where computers are accommodated in a network connection apparatus called “a LAN switch” by using twist-pair cables. When two apparatuses re called hereby the “apparatus A” and “apparatus B”, the able that connects these apparatuses A and B includes a plurality of transfer paths. When the apparatuses A and B communicate with each other, the transfer path for transmitting data from the apparatus A to the apparatus B and the transfer path for receiving data by the apparatus A from the apparatus B are mutually independent transfer paths. A 10 Base-T technology, for example, uses the twist-pair cable. In this twist-pair cable, two conductors form a pair of transfer paths and a plurality of pairs are incorporated in one cable. One of the pairs is used for transmission and another pair, for reception. A technology called “100 Base-FX” uses an optical fiber cable. This optical fiber cable incorporates a plurality of optical fibers. One of the optical fibers is used for transmission, and another for reception.
The communication system described above has a setup for detecting whether or not the two apparatus connected by the cables are under the communicable condition. In other words, the apparatus A not only transmits data to the transfer path for transmitting the data to the apparatus B but transmits either periodically or steadily a specific signal different from the data during the period in which it does not transmit the data. On the other hand, the apparatus B always monitors the transfer path for receiving the data, detects the data or the specific signal different from the data transmitted from the apparatus A and thus confirms that data can be transmitted from the apparatus A to the apparatus B. A signal called “link pulse” is mainly used in the system using the twist-pair cable. In a system that uses the optical fiber cable, there is a method that utilizes an idle signal sent for reproducing the reception clocks. Receiving these signals, the apparatus B can know whether or not the apparatus A and the transfer path for transmitting the data from the apparatus A to the apparatus B operate normally. A similar processing is executed, too, on the transfer path for transmitting data from the apparatus B to the apparatus A. In consequence, it is possible to know that the transfer paths between the apparatus A and the apparatus B are connected correctly and that no failure occurs in the mating apparatus, hence the apparatuses A and B are under the communicable condition.